Yes will become too small for GF.
Should be good for a Blue Crayfish! To make it interesting, they like caves, tunnels, DW, rocks and may chop up plants, but stem plants should recover and grow back, and if it gets pulled out of the substrate, then it can easily be replanted.
***Edit also they can crawl out so be aware of their amazing escaping abilities!!!!!
Common GF can get 12-14 inches in a normal environment. A pond is a good option for the common's future.
Does your blue "lobster" have a name yet?